We study the phase-separation dynamics of a two-dimensional Ising model whe
re A and B particles can only exchange position with a vacancy. In a wide r
ange of temperatures the kinetics is dominated, during a long preasymptotic
regime, by diffusion processes of particles along domain interfaces. The d
ynamical exponent z associated to this mechanism differs from the one usual
ly expected for Kawasaki dynamics and is shown to assume different values d
epending on temperature and relative AB concentration. At low temperatures,
in particular, domains grow as t(1/2), for equal AB volume fractions.